A zoom lens assembly comprises a collection of optical components that can be moved relative to each other in order to vary the effective focal length and field of view of the assembly. For example, a simple zoom lens assembly may comprise a pair of lenses (or lens groups) that can be moved apart along a common optical axis to increase the assembly's focal length while decreasing its field of view (“zoom in”), and brought closer together along the axis to decrease the assembly's focal length while increasing its field of view (“zoom out”).
Zoom lens assemblies can be found in a wide variety of optical instruments, including, for example, cameras, bar-code scanners, binoculars, telescopes, microscopes, and projectors, to name but a few. In addition, the number, type, and spacing of lenses in a zoom lens assembly can vary widely across different applications. For instance, different optical applications may use diverging and/or converging lenses, magnification lenses, focus correction lenses, and so on. Moreover, the lenses in a zoom lens assembly may be combined with a variety of other optical components such as optical filters, mirrors, and so on, depending on the application in which the zoom lens assembly is used.
As an example, FIGS. 1A and 1B show a simple zoom lens assembly used in a camera 100. In camera 100, as a first optic 105 moves relative to a second optic 110, the zoom lens assembly “zooms out” or “zooms in” to shrink or enlarge the projection of an image onto a projection plane 130 such as film or a CCD or CMOS image sensor.
In most conventional zoom lens assemblies, lenses and other optical components are moved under the control of a collection of mechanical components such as motors, switches, solenoids, and/or other actuators (not shown in FIGS. 1A and 1B). Accordingly, the performance and reliability of these assemblies tends to be affected by the performance and reliability of the mechanical components. For instance, the speed and precision with which a zoom lens assembly can zoom in and out is generally determined by the response-time and accuracy of the mechanical components. Similarly, the lifetime of a zoom lens assembly may be tied to the lifetime of the mechanical components.
Unfortunately, conventional mechanical components tend to suffer from a variety of shortcomings that can limit both the performance and reliability of zoom lens assemblies. For instance, motors used to move the lenses may experience some form of gear lash and/or hysteresis, which may affect the accuracy of their movement. In addition, many of the mechanical components may fail much more readily than corresponding optical components, thus limiting the expected lifetime of the zoom lens assemblies according to the failure characteristics of the mechanical components. Further, mechanical components may limit the degree to which the zoom lens assemblies can be miniaturized. For instance, while it may be possible to develop tiny lenses for miniature zoom lens assemblies, it may not be feasible to create commensurately tiny motors and other actuators for moving the lenses. Accordingly, conventional zoom lens assemblies may not be able to fit within small electronic devices such as miniature cell-phone cameras and bar code scanners. Finally, mechanical actuator components such as motors typically consume a relatively large amount of power compared with other components of a zoom lens assembly. Accordingly, the power consumption of the mechanical actuators may not be acceptable for portable devices where power is scarce, such as the cell-phone cameras and portable bar code scanners.
In an attempt to address at least some of the above shortcomings of conventional zoom lens assemblies, researchers have sought new techniques for moving the lenses and other optical components of a zoom lens assembly. One such technique involves the use of a shape memory alloy that expands and contracts when heated and cooled to move one of two lens groups within a zoom lens assembly. An example of a camera using this technique is disclosed in U.S. Patent Application Publication No. 2007/0058070 to Chen (hereafter, “Chen”).
Like the conventional mechanical components described above, the shape memory alloys used in zoom lens assemblies such as that illustrated in Chen also suffer from a variety of shortcomings. For instance, the amount of displacement provided by these shape memory alloys is relatively small compared to their overall size. In particular, conventional shape memory alloys such as those described in Chen can typically be expanded by around 10% of their original size when heated. Accordingly, in order to achieve even a relatively small amount of lens displacement (e.g., 0.5 cm), Chen requires a zoom lens assembly to include a relatively long unit of shape memory alloy (e.g., 5 cm). Additionally, the heating and cooling of the shape memory alloy can be a relatively slow and power consuming process. Finally, the shape memory alloys in Chen tend to exhibit hysteresis characteristics that may limit the precision with which they may displace the lenses in a zoom lens assembly.
The need exists for techniques and technologies that overcome some or all of the above problems, as well as ones that provide additional benefits. Overall, the examples herein of some prior or related technologies and their associated limitations are intended to be illustrative and not exclusive. Other limitations of existing or prior technologies will become apparent to those of skill in the art upon reading the following Detailed Description.